1. Field of the Invention
The present invention relates to a foreign matter removal unit for eliminating foreign matter such as dust and the like, and an optical apparatus having the same.
2. Description of the Related Art
Optical apparatuses such as digital cameras or the like which perform imaging by converting a subject image into electrical signals receive a photography light flux with an imaging device, and convert photoelectric conversion signals output from the imaging device into image data. With such imaging apparatuses, optical low-pass filters and infrared ray absorbing filters are disposed on the subject side of the imaging device. In the event that foreign matter such as dust or the like adheres to the face of these filters, the portions in the photographed image where the adhesion has occurred appears as black spots, deteriorating the appearance of the image. Particularly, with digital single-reflex cameras with exchangeable lenses, mechanical moving parts such as the shutter and quick return mirror are disposed in close proximity to the imaging device and there are cases where foreign matter such as dust that has originated at these moving parts adheres to the surface of the imaging device or filter. Also, foreign matter such as dust may enter the camera body from the lens mount opening when exchanging lenses, and adhere to the surface of the imaging device or filter.
There is known a way to avoid such phenomena by vibrating the optical filters provided at the subject side of the imaging device using a piezoelectric device, so as to remove foreign matter such as dust which has adhered to the surface of the optical filters.
At this time, to effectively remove foreign matter such as dust, the optical filter is preferably vibrated at a resonant frequency of the optical filter by the piezoelectric device, so as to increase the amplitude of the vibrations. However, the resonant frequency differs depending on the external shape of the optical filter, the thickness thereof, physical property parameters, and so forth, so the resonant frequency for each optical filter differs due to variation in fabrication precision, manufacturing processes, and so forth.
Accordingly, with the invention disclosed in Japanese Patent Laid-Open No. 2009-17461, a piezoelectric device is disposed nearby one side of a rectangular optical filter, so as to be parallel to that side. Further, to detect the vibration state of the optical filter, one detecting electrode is disposed on the piezoelectric device separately from an electrode for driving, and one detecting ground electrode is disposed on the back face thereof. The resonant frequency is searched for while monitoring the electrode voltage thereof, the optical filter is vibrated using the found resonant frequency, and dust and the like adhering to the surface of the optical filter is removed.